LONDON, Sept 9 (Reuters) - Poor U.S. job figures for Augustmake it more likely that the Federal Reserve will take out extrainsurance this week against an economic relapse by plumping forfresh monetary stimulus.

With Chinese growth slowing markedly and the euro zone miredin recession, the United States is resuming its traditional roleas a motor - though not a high-powered one - for the globaleconomy.

That is weak enough in the eyes of many economists totrigger a third round of asset purchases - or quantitativeeasing in market jargon - by the U.S. central bank, to bringdown bond yields and perk up investors and companies.

A Reuters poll of 59 economists after the jobs reportrevealed a 60 percent chance of such action at the Fed's Sept.12-13 policy meeting. A poll on Aug. 24 had put the likelihoodat 45 percent

"It makes the forecast pretty easy that the Fed will move,"said Bruce Kasman, an economist with J.P. Morgan in New York."We think the case has certainly been sealed."

Kasman expects the Fed to buy another $200-$300 billion ofbonds and to extend its forecast that short-term interest rateswill stay near zero from late 2014 into 2015.

Jan Hatzius with Goldman Sachs had not been expecting theFed to ease further before the end of the year.

But he now sees a greater than 50 percent chance it willannounce on Thursday that it will buy about $50 billion of bondsa month, mainly mortgage-backed securities, with the end date ofthe programme dependent on how the economy evolves.

The main U.S. data of the week will come on Friday. Retailsales probably rose 0.7 percent in August and industrial outputjust 0.1 percent, according to a Reuters survey of economists.

ALL EYES ON TOP GERMAN COURT

Europe has a light calendar of timely economic data - thereis a batch of backward-looking euro zone figures for July - buta crowded schedule of political events, including Dutchelections on Wednesday and a meeting of European financeministers on Friday.

Top of the list is a ruling by Germany's constitutionalcourt on Wednesday on a motion to block the establishment of theEuropean Stability Mechanism, the euro zone's new, permanentrescue vehicle.

Legal experts interviewed by Reuters all expect the court toapprove the fund, but they also believe it will impose toughconditions limiting Berlin's flexibility on future bailouts.

The verdict could contain some "unpleasant surprises" forinvestors, said Holger Schmieding, an economist with BerenbergBank in London.

That could have serious repercussions for the plan unveiledlast week by European Central Bank President Mario Draghi forsecondary-market bond purchases to lower what the bank sees asunjustifiably high yields on the debt of countries such as Spainand Italy.

Markets cheered Draghi for reducing the tail risk of thebreak-up of the single currency.

But the initiative hinges on struggling euro zone membersapplying for aid from the ESM or its current precursor fund,which would back up the ECB by buying those governments' bondswhen they are auctioned.

So no ESM, big problem.

Even if Germany's top court does not throw a spanner in theworks, Draghi's gambit will not magically restore the Europeaneconomy to health, said Andrew Milligan, head of global strategyat insurer Standard Life in Edinburgh.

"There is probably going to be some helpful impact forEuropean industry in terms of lower yields and a boost toconfidence, but from a growth point of view, this is not a gamechanger," Milligan said.